The upheaval in the American financial system sent shock waves through the stock market Monday, producing the worst day on Wall Street in seven years as investors digested the failure of one of its most venerable banks and wondered which domino would be next to fall.

The upheaval in the American financial system sent shock waves through the stock market Monday, producing the worst day on Wall Street in seven years as investors digested the failure of one of its most venerable banks and wondered which domino would be next to fall.

The shotgun-wedding deal in which JPMorgan Chase agreed to buy Bear Stearns for a pittance isn't even 3 days old and is being challenged by one of Bear's biggest shareholders. But that hasn't prevented observers from branding it one of the most significant transactions in the history of Wall Street, on par with J. Pierpont Morgan's bailout of a failing bank in 1907, a move that is believed to have prevented a market failure at that time.

Citigroup said it will do business as "Citi" and sell its trademark red umbrella log, hoping to add customers and sell more products with a uniform marketing strategy. Its legal name will remain Citigroup Inc.